js实现点击注册按钮开始读秒倒计时的小例子

<script language="javascript">
<!--
var wait_time = 8; //设置秒数(单位秒)
var secs_time = 0;         
for(var i=1;i<=wait_time;i++)
{
 window.setTimeout("sTimer("+i+")",i*1000);
}
function sTimer(num)
{
 if(num==wait_time)
 {
  document.getElementById("reg_btn").value=" 同意注册 ";
  document.getElementById("reg_btn").disabled=false;
 }
 else
 {
  secs_time=wait_time-num;
  document.getElementById("reg_btn").value="请先阅读服务条款 ("+secs_time+")";
 }
}
//-->
</script>

<div style="width:350px; text-align:center;">
<form name="regForm" method="post" action="">
<input type="submit" value="请先阅读服务条款 (0)" disabled="disabled" id="reg_btn">
<input id="BtnClose" type="button" value=" 我不同意 " onclick="window.close();">
</form>
</div>